The invention concerns a method for high resolution NMR (=nuclear magnetic resonance) measurements comprising the application of excitation pulses and the acquisition of data points, whereby a dwell time Δt separates the acquisition of two consecutive data points. A method as described above is known from Andrew E. Derome, “Modern NMR Techniques for Chemistry Research”, Pergamon Press, 1987.
Double-resonance techniques were first introduced into high-resolution CW-NMR by Bloch in 1954.[1] Bloom and Shoolery[2] have shown that the application of an rf field B2 to 31P nuclei such that γB2>>2π|J| can lead to the collapse of the doublet in the 19F spectrum arising from a heteronuclear coupling J(31P-19F). Freeman and Anderson[3, 4]proposed a theoretical description that is applicable to spin systems with either homo- or heteronuclear couplings and explains the spectral complexities and multiplicities arising from the secondary rf field B2 while sweeping the frequency of the main rf field B1 to observe the response in CW (=continuous wave) fashion. In particular, information about the topology of non-degenerate energy levels and the relative signs of coupling constants can be extracted.[5, 6]A detailed discussion of these effects, which have later become known as “spin tickling” experiments, has been presented elsewhere.[7, 8] Ever since, the development of advanced methods for the characterization of more and more complex systems (often in biomolecules) has been accompanied by a desire to achieve a gain in resolution and spectral simplification. The removal of homonuclear scalar interactions can simplify assignments in overlapping regions in both 1D and 2D spectra, and a number of methods have been proposed to eliminate the fine structure due to J-couplings.[9-15] However, none of these methods appear to have found widespread applications. Moreover, they usually only achieve a decoupling effect in the indirect dimension of 2D spectra. A method similar to the above is known as homonuclear decoupling, where a weak rf field of constant amplitude is applied throughout the observation of the signal. This method suffers from problems of interference between rf irradiation and signal observation, and is difficult to extend to multiple frequencies.
The object of the present invention is to present an effective and fast method of decoupling of homonuclear couplings.